Apparatuses consistent with the present invention relate to heat exchangers capable of heat exchange among three or more fluids.
The heat exchanger is a device for transferring heat energy from a high-temperature fluid to a low-temperature fluid, and is typically employed as a heating, cooling, or heat recovery device of various kinds in a chemical treatment system. For example, hydrogen for use in a fuel cell may generally be produced by subjecting hydrocarbon fuels (feedstocks) such as natural gases to reforming and other treatments, and a fuel reforming system for such a reforming treatment requires several types of heat exchangers. The heat exchangers for use with the fuel reforming system may include, for example: an air cooler for cooling high-temperature and high-pressure air used for reforming treatment and discharged from a compressor to render it reusable as air for driving auxiliary equipment; a gas cooler for cooling a high-temperature reformed gas generated in a reformer; and a superheater for superheating a steam fuel mixture made from steam mixed with air and natural gases.
Typically, the heat exchanger is provided for causing heat exchange to take place between two fluids (e.g., gas and gas, liquid and liquid, gas and liquid, etc.). For systems or devices that require a plurality of heat exchangers, however, is employed an integrated heat exchanger in which a plurality of fin-and-tube type heat exchangers are combined together in order to achieve reductions in footprint and manufacturing cost. By way of example, a heat exchanger making up an air conditioner/water heater of an engine-driven heat pump type is known in the art (see JP 7-4778 A, Paragraph 0013, FIG. 2), which includes three heat exchangers combining to form a single unit: a heat exchanger for a coolant, a radiator, and an outdoor heat exchanger for a refrigerant. The heat exchanger for a coolant transfers heat between the refrigerant and the coolant for cooling an engine that causes a compressor of a refrigerant circuit to do mechanical work. The radiator transfers heat between the air and the coolant for cooling the engine. The heat exchanger for a refrigerant transfers heat between the air and the refrigerant. Another example of the integrated heat exchangers known in the art is a heat exchanger making up an industrial machine, which includes an after cooler for cooling compressed air and an oil cooler for cooling engine oils or the like, combining to form a single unit (see JP 10-213382 A, Paragraph 0018, FIG. 1).
Since the above-described integrated heat exchangers are each designed to form a single unit by simply combining two or more heat exchangers together, heat exchange among three or more fluids could not be achieved in the single-unit heat exchangers without increasing the heat exchange volume.
In the heat exchangers for use with the fuel reforming system as described above, the heat exchanger for cooling the reformed gas generated in the cylindrical reformer with a coolant is preferably designed in a cylindrical shape such that the reformed gas is flowed in its axial direction because such a cylindrical shape serves to maintain the continuity of the passage of the reformed gas and conforms to the requirements imposed on the system layout. In this configuration, a plurality of pipes through which the reformed gas is flowed are disposed within a cylindrical container in which the coolant is flowed, which would increase the amount of the coolant existing in the heat exchanger and would thus require an extended period of time for warming up of the fuel reforming system, disadvantageously decreasing the operation efficiency of the fuel reforming system. Moreover, in this type of the heat exchanger, the cylindrical container would inevitably be large in volume, which would make it difficult to improve the heat exchange performance by increasing the flow rate of the coolant flowed in the cylindrical container. It could be conceivable that the flow rate of the coolant would be increased by providing baffle plates spaced at small spacings in the cylindrical container, but this would increase the pressure loss of the coolant in the cylindrical container, thus causing disadvantageous increase in the load and power consumption of the circulating pump.
Still another example of the integrated heat exchangers known in the art, which appears not to entail the above disadvantages, is a laminated board type heat exchanger making up a helium liquefier/refrigerator or the like, which includes a plurality of porous thermally conductive boards and a plurality of thermally insulating boards with hydraulic passages provided therein. The thermally conductive boards and the thermally insulating boards are laminated alternately, and two channels of hydraulic passages piercing through the laminated layers are formed so that heat exchange takes place between two fluids through the thermally conductive boards while heat transfer across the laminated layers (i.e., between adjacent thermally conductive boards) is blocked by the thermally insulating boards. In addition to the two-channel hydraulic passages for heat exchange, another hydraulic passage through which a precooling refrigerant is passed for heat exchange is formed approximately along the central axis piercing through the laminated layers (see JP 6-55070 U, Paragraphs 0011, 0012, FIG. 1).
This type of the integrated heat exchanger however has the following disadvantages in production process and in reliability of the product. In the production process, a laminated body (composed of elements of several kinds to achieve a desired heat exchange capability) is manufactured by laminating the porous thermally conductive board and the thermally insulating boards alternately with adhesive sheets interleaved between adjacent boards. Therefore, each of the elements should be formed to have holes that constitute the hydraulic passages when the elements are assembled, and should be assembled in such a manner that the angular phases of the elements are accurately aligned with each other; thus, special working tools and assembly devices are required. Moreover, the multilayer structure of this heat exchanger is produced by bonding the alternately stacked porous thermally conductive boards and thermally insulating boards with the adhesive sheets, and thus could hardly avoid incomplete bonding which would entail leakage and/or mixture of the fluids, or other undesirable consequences. To be more specific, there is a potential of peeling or the like as a result of degradation of the adhesive which would progress as the laminated body carries high-temperature fluids over a long period of time.
The present invention has been made with consideration given to the above-discussed disadvantages. The inventors has recognized that it would be desirable to provide a heat exchanger having a relatively simple structure and capable of highly efficient heat exchange among three or more fluids.
Illustrative, non-limiting embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an illustrative, non-limiting embodiment of the present invention may not overcome any of the problems described above.